The present invention relates to a method for lining an inner surface of a service pipe branched from a pipeline such as a gas main and a water main buried under a road. Due to deterioration of the pipe, it is necessary to line the inner surface of an old pipe with coating material such as resin.
In a known method of lining the service pipe with resin, the resin is injected from one end of the service pipe thereby rendering the resin to adhere on the inner surface of the pipe. The excessive resin which did not adhere thereon is retrieved from the other end. In order to carry out the repair, the roads must be dug up to expose the connection between the main and the service pipe which is to be treated, and the pipe disconnected from the main. The operation involves blocking of the traffic, and furthermore after the repair, joining the pipe to the main and mending the roads. Hence, the repair requires much labor, time and cost.
The applicant of the present invention has proposed in Japanese Patent Application Laid-Open 4-114773, a method for lining pipes without causing these problems. The method comprises a first step where a necessary amount of resin interposed between lining pigs in a mass is charged from an end opening of a service pipe and carried toward a gas main by injecting compressed air. In a second step, the resin is sucked from the end opening, thereby lining the wall of the pipe. Such a repairing operation can be efficiently performed without causing the above-described problems.
However, since the mass of resin is forward pushed by the compressed air, the mass is subjected to various changes of pressure caused by the compressed air. Namely, if the inner diameter of the pipe is locally small or large, the pressure of air changes when passing the irregular portions, causing the resin to be abruptly pushed forward. As a result, a part of the resin may erupt out through a gap formed about the lining pig at the front end of the mass and flows into the gas main.
Another problem of the conventional method is that there is no correlation between the quantity of the injected air and a travelling distance of the resin because the air is compressible. Accordingly, it is impossible to detect the front end position of the resin mass from the air quantity. As a result, an expensive device, such as a sonic probe, must be provided to detect the location of the front end of the resin mass, so that the cost of the repairing system increases.